In internal combustion engines, particularly in four-cycle engines or the like for example, a transmission mechanism for transmitting rotation of a crankshaft to camshafts is configured to provide a chain tensioner on the slacking side of a chain, so as to exert a regulative force of the chain tensioner to a chain, to thereby keep the tensile force of the chain at a constant level.
A general chain tensioner is configured to have a spring and a plunger assembled in a cylinder formed in a housing. When the chain slacks, the chain tensioner operates to allow the plunger, urged by the spring, to pressurize the chain so as to keep an appropriate tension, whereas when the chain produces tension as large as pressurizing the plunger, the chain tensioner operates so as to buffer regression of the plunger, with the aid of hydraulic pressure of a hydraulic oil filled behind the plunger.
This sort of chain tensioner, configured to urge the plunger using the spring, needs a mechanism for preventing projection of the plunger during the rest time typically in the process of delivery. Known exemplary mechanisms of suppressing the plunger having conventionally been adopted in general, include a mechanism of preventing projection of the plunger, by providing through-holes to the plunger and the housing, and setting a pin by inserting it through the individual through-holes so as to prevent projection of the plunger; and a mechanism of providing an engagement groove to the plunger, and engaging a projection preventive plate attached while being mediated by a pin with the engagement groove, so as to prevent projection of the plunger (see Patent Document 1, for example).
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2005-344872
The conventional mechanisms for preventing projection of the plunger, however, needs a large number of components, and needs also spaces allowing piercing or grooving of the plunger, raising obstacles to downsizing of the chain tensioner. As for the chain tensioners using the pin as described in the above, those once detached from an engine typically for maintenance will necessarily be attached by re-setting the pin so as to prevent the plunger from projecting, and are therefore not understood that they are ready to handle.
The present invention was conceived after considering the above-described situation, wherein an object of which is to provide a chain tensioner having a compact and simple structure, and excellent in the handlability.